Ok, I have a pretty good understanding of how to set up my battery bank for my trolling motor to get 24V out to trolling motor, my question is if I want to run it in 12V mode, how do i get my batteries to only push 12V when they are set to run a 24V circuit?

Here is a picture of the plug in, it is 3 prong, and the 3 wires that connect to batteries....I understand one connects to the 24V side of the batteries...but to draw the 12V side, do I connect to the first batteries positive so it is only 12?

Also...how do I figure out which of these 2 positive leads is supposed to supply the 24V or 12V side so i hook it up right?

And just exactly what motor are we talking about? They are not all the same. Little details such as is there a 12/24 selector switch on the foot pedal of the motor. Or is there a 12/24/Run/Charge switch on the panel at the bow of the boat. How this switching gets done can take on many forms. So here is what you need to do:
1) Look at the plug on the motor and draw yourself a picture noting the wire colors for the three terminals. They will typically be red, orange and black, or red, orange and white. Red is typically +24 volts, orange is typically +12 volts, and white or black is typically ground.
2) Now match the motor plug terminals to the terminals in the receptacle and mark those as +12, +12 and ground respectively
3) Set up the batteries like shown in the diagram below. WARNING: If your motor wire colors are different than those shown you need to contact the manufacturer to determine which is +24 and which is +12 and which is ground. What the colors are on the receptacle is not of concern as you just need to match the terminals.

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Doing my due diligence and looking to see what wires go where, just made me feel like a ditz lol...thanks for your quick and informed reply, but apparently it is only a 12V trolling motor..peeled back some tape on the trolling side of plug, and it had the 3 colors you mentioned...but decided to peel it back farther and realized only a red and black were connected, the 3rd wire was just hanging loose....

may have been a 12/24 originally on the boat but the replaced with a 12V...sorry about that, I should have thought to cut that tape back earlier...I have had wiring like this throughout the project and removed every wire and ran new stuff for peace of mind...why I did not check the trolling side of that plug I don't know lol

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OK -- just don't connect that motor to a 24 volt system. You would have to parallel the two batteries like shown below if you feel you actually need the run-time two batteries in parallel provide. This system is still 12 volts but doubles run time.

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Your statement that "apparently it is only 12v" makes me believe you are not 100% sure. Are you assuming that because there are only two wires on the TM side of the plug that it is 12v only? It may have been a 12/24 changed to a 24v only. Do some research on the model number to ensure it is a 12v only TM. I have the knack for missing the obvious, so if I have in this case my apologies.

D-Dubya

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OK -- just don't connect that motor to a 24 volt system. You would have to parallel the two batteries like shown below if you feel you actually need the run-time two batteries in parallel provide. This system is still 12 volts but doubles run time.

I will still use 2 batteries, and leave my wiring for a 24V upgrade later should I choose to, thanks again for the replies, reading your posts has helped me immensely in rewiring my boat...nothing is powered on yet, I am just pulling wires and routing them in the cap since once it is flipped and replaced I cant get to that stuff again....the original wiring looked ok, but not knowing what goes where was more confusing than just a complete tear out and using new wire redo it.

Your statement that "apparently it is only 12v" makes me believe you are not 100% sure. Are you assuming that because there are only two wires on the TM side of the plug that it is 12v only? It may have been a 12/24 changed to a 24v only. Do some research on the model number to ensure it is a 12v only TM. I have the knack for missing the obvious, so if I have in this case my apologies.

It is a MotorGuide III Model #2600....Again with assumption because I was told it was original to the boat (trailer, boat and engine were all verifiable as 1982 models). I got this boat from the original owner's son after he passed away, The OP bought it showroom new, but the son allowed it to sit out in a field for quite a few years. So as to whether it is 12 or 24 I am not sure, it does have a switch on foot pedal (cant read the plate) which I assumed was the 12/off/24 3 position switch

I have looked everywhere for a manual, for this old model, with no luck. I plan to freshen it up on appearance and use it til I can afford a newer one...spending a lot on the actual restore right now.

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It's most likely 12V, 26# of thrust. The switch on the foot pedal is probably for continuous/off/momentary.

Bob, Orange County NY
'88 Bayliner 1700 Capri Bowrider, 85 HP Force O/B, "Sea Weasel"
Want a vessel safety check? Click here. Want to join the Coast Guard Auxiliary? Click here.Disclaimer: Although I am a member of the USCG Auxiliary, the opinions and advice in my replies are my own and do not necessarily reflect CG or CG Auxiliary policy or regulations unless so specified.

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Ran into troubles a few times going dual battery and learned the hard way to never use mis-matched batteries (Output Ratings) or they'll go dull and live a much shorter life. Same make, model and CCA rate are best when used in series or parallel, in my opinion and experience.

Marine Usage: Fuse-it, Solder-it, Seal-it.

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It doesn't matter in a series connection if the batteries are mismatched in age, brand, CCA, AHr, RC, group size or any other measure as the system will provide 24 volts. The only down-side is that capacity (run time) will be only as long as the lowest spec battery can provide. Using mismatched batteries in parallel has the same characteristics however the run time now will include "equalization" which means the weaker battery of the two will draw down the stronger until the two are equal. At that point they will discharge equally. Battery longevity (service life) is not significantly shorter in either application. Improper maintenance and charging techniques kills more troller batteries than a mismatch.

As I have explained, I have had bad experiences with mis-matched batteries, the cost of replacement was not worth the risk.
Scott

The automotive article you reference is not a realistic conclusion about mismatched batteries. In the case of a jump start pack, there is obviously a mismatch in capacity (AHr) ratings yet a small jump start pack will start a partially discharged vehicle battery. It will NOT start a totally dead/bad vehicle battery. Measuring voltage with two batteries that are not equally charged will of course measure lower than 12.6 because of the "equalization" I spoke of. As is the case of the diesel truck -- one of the batteries was dead (as in a bad battery). A partially discharged battery in a series string cannot kill the other battery. In a parallel system -- yes they will equalize. A bad battery in a parallel setup may indeed kill the other battery but that is not a condemnation of a parallel setup or mismatch. In your experience you very likely had one "bad" battery. The other battery didn't kill it nor did the mismatch. Having owned many diesel vehicles with parallel batteries I can say also from experience that as long as you keep two "good" batteries in a parallel system, they will work just fine. Obviously the lesser capacity of the two must still have specs higher than the current draw of the electrical system. No system -- series or parallel can operate proplerly if one battery cannot hold or accept a full charge. That's not what this discussion is about. In a single battery system you quickly notice a loss of performance and the battery gets replaced. People tend to ignore the situation in a dual battery situation and hence get wrapped around the axle with this mismatch situation.

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Not that it pertains much to my original post but i will put you at ease and say the batteries will be duplicate, but I believe Silvertip is spot on, as a truck driver for many years..it was not uncommon for me to only have 1 of my 4 batteries go dead and need replacing while the other 3 were just fine...

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One more tidbit then I'm outa here. I jump started a Peterbuilt last summer that had six batteries in parallel. There were no matching labels on any of the batteries. The driver admitted that he replaced one of them just days before as he had all six load tested and found the bad one. Why was it dead now? Because the one he used as a replacement was also questionable and he thought that one might be bad as well as it was one he had "laying around". So again -- "bad" batteries make a bad system -- differng capacities does not.

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Sorry about the confusing link, but I'm sure we know what I'm talking of. I'll put it another way, in my opinion, never hook any batteries up in parallel unless it's necessary and short term. If your running a boat (or vehicle), with a high amp recharging circuit.

Why?, if one of the batteries requires less charge than the other the charging source may ignore that and continue charging based on lower voltage readings. Hence creating an overcharge condition of the fully-charged battery that could eventually lead to short-term death. Though it's more of an investment, a battery switch is the ticket and if charging from a heavy output charger, such as a 55+ amp alternator as on inboard/inboard outboard engines, use a battery isolator. They didn't invent battery: switches and isolators for nothing.

I write the above with all respect to senior members opinons that differ.